The present invention pertains to roller cone type drill bits or "rock bits," e.g. as are used for drilling oil and gas wells. More specifically, such bits have a plurality of cones, usually three, rotatably mounted on respective legs of a bit body. As the bit body is rotated along with the drill string, the cones roll along the bottom of the hole, generally breaking up the rock by a crushing action (by way of contrast, for example, to drag type bits, which typically have no relatively moving parts and break up the rock by a scraping action).
Traditionally, the bit body of such a roller cone type drill bit is formed by welding together three elongate sector-like pieces along longitudinally extending juncture lines, each of the pieces including one leg of the bit and a one-third sector of the remainder of the bit body. An example may be seen in prior U.S. Pat. No. 4,187,743. Each of the three pieces is formed by forging, with the parting line of the forging dies, and thus the flash line of the forging, running generally parallel to the length of the work piece, and of the bit body to be formed therefrom.
It has also been known to form bit bodies by welding leg portions onto a main body portion along generally transverse or horizontal lines. An example is given in U.S. Pat. No. 4,694,551.
In U.S. Pat. No. 4,711,143, there is shown an improvement over such horizontal welding methods wherein the surfaces of the main body to which the leg portions will be welded are disposed at a non-perpendicular angle to the centerline, more specifically located on a common conical locus, and the surfaces of the leg portions to be welded thereto are correspondingly formed to mate with the main body along that locus. Although U.S. Pat. No. 4,711,143, allows for the invention thereof to be applied to main bodies of new manufacture, that invention was originally developed in connection with an operation of salvaging parts of used bits and forming new bits from them. In practice, the main body was one of the salvaged or premanufactured parts. Thus, aside from the machining of this main body to provide the aforementioned conical surface, and other operations necessary to adapt it to the method of said prior patent, no detail is given as to the method of original manufacture of the main body portion of the bit. Indeed, as practiced by assignee and its predecessor(s) in interest, the main body was a salvaged part made of three sector-like pieces, as described above.
U.S. Pat. No. 4,694,551, states, in theory, that entire main bodies (for welding to leg extensions) could be cast or forged. However, this patent neither recognizes nor addresses the practical problems of forging a main body in one piece. To applicant's knowledge, no such bodies were forged prior to the present invention. Assignee made one such bit body by casting, as an experiment in approximately 1990. A salvaged three-sector body was used to make the mold for this casting.